Influence of Position and Flow Rate of Infiltrated Air on NO x Emission Characteristics in Methane-Oxygen Combustion : A Numerical Study

In pure O₂ combustion, the absence of N₂ in the fuel theoretically eliminates the emission of NOx. However, when CH₄ combusts in the presence of O₂ in a reheating furnace, the influx of external air into the furnace introduces N₂, resulting in a significant emission of NOx. Therefore, in this study, we numerically investigated the effect of external-air intrusion on the production of NOx during CH4-O₂ combustion through computational fluid dynamics simulation. NOx emission characteristics were investigated in terms of the location and amount of external-air inflows. Results indicated that NOx emissions increased when external air flowed into the main combustion area where the temperature was high. Additionally, the flow rate of external air exhibited different effects on NOx emission characteristics depending on the inflow path of the air. When external air was introduced near the burner, the NOx emission concentration increased as the flow rate of the air decreased.